Jf. Quignard et al., Potassium ions and endothelium-derived hyperpolarizing factor in guinea-pig carotid and porcine coronary arteries, BR J PHARM, 127(1), 1999, pp. 27-34
1 Experiments were designed to determine in two arteries (the guinea-pig ca
rotid and the porcine coronary arteries) whether or not the endothelium-der
ived hyperpolarizing factor (EDHF) can be identified as potassium ions, and
to determine whether or not the inwardly rectifying potassium current and
the Na+/K+ pump are involved in the hyperpolarization mediated by EDHF.
2 The membrane potential of vascular smooth muscle cells was recorded with
intracellular microelectrodes in the presence of N-omega-L-nitro-arginine (
L-NA) and indomethacin.
3 In vascular smooth muscle cells of guinea-pig carotid and porcine coronar
y arteries, acetylcholine and bradykinin induced endothelium-dependent hype
rpolarizations (-18+/-1mV, n = 39 and - 19 +/- 1 mV, n = 7, respectively).
The hyperpolarizations were not affected significantly by ouabain (1 mu M),
barium chloride (up to 100 mu M) or the combination of ouabain plus barium
.
4 In both arteries, increasing extracellular potassium concentration by 5 o
r 10 mM induced either depolarization or in a very few cases small hyperpol
arizations which never exceeded 2 mV.
5 In isolated smooth muscle cells of the guinea-pig carotid artery, patch-c
lamp experiments shows that only 20% of the vascular smooth muscle cells ex
pressed inwardly rectifying potassium channels. The current density recorde
d was low (0.5+/-0.1 pA pF(-1), n = 8).
6 These results indicate that, in two different vascular preparations, bari
um sensitive-inwardly rectifying potassium conductance and the ouabain sens
itive-Na+/K+ pump are not involved in the EDHF-mediated hyperpolarization.
Furthermore, potassium did not mimic the effect of EDHF pointing out that p
otassium and EDHF are not the same entity in those arteries.